24 volt computer fan

Hi . My system was 12 volts with a 12 volt rv water pump. Strapped to the top of the pump i had a 7 watt 12 volt fan . This worked for 10 years or so, i think keeping the motor cool helped .
I have done a change to 24 volts now . considered a voltage step down unit for the 12 volt pump, however considering its age, got a new 24 volt pump. To this i added a 24 volt fan. . have had 2 of these fans fail, i think maybe because of the increased voltage above the 24 volts . ie 29 volts for absorb.
So ....... think a resister in series with the fan may help , or a voltage regulter . What size resister ? or would i be better with a small regulator circuit ?
Any help would be appreciated
Regards Peter
I have done a change to 24 volts now . considered a voltage step down unit for the 12 volt pump, however considering its age, got a new 24 volt pump. To this i added a 24 volt fan. . have had 2 of these fans fail, i think maybe because of the increased voltage above the 24 volts . ie 29 volts for absorb.
So ....... think a resister in series with the fan may help , or a voltage regulter . What size resister ? or would i be better with a small regulator circuit ?
Any help would be appreciated
Regards Peter
2225 wattts pv . Outback 2kw fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts in 2 volt Shoto lead carbon extreme batterys. off grid holiday home
Comments
For example if 1/4 amp fan and you want 30-24=6 volt drop:
V=IR, R=V/I = 6 volts / 0.25 amps = 24 ohms
P=V*I= 6 volts * 0.25 Amps = 1.5 Watt minimum resistor size/power rating
i don't think it will hurt the fan to use an in-line resistor... May start a little slow and may run a little slower RPM.
Does the water pump run long enough to get hot? Most DC RV pumps use brushed motors--And frequently the brushes wear out--And you can replace them sometimes (depending on motor design).
-Bill
Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.
Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.
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